Add errors for redundancy in the domain and problem file

[drexlerd]

During parsing, we can collect additional information such as: what requirements, objects, predicates, function skeletons, etc. were actually used and provide a errors to the user.

[drexlerd]

Before closing a scope, we need to know the PDDL objects that were referenced, then we can check whether all required objects were referenced at least once. Hence, the scoping mechanism must get the ability to return PDDL objects.